Support streaming conformer CTC models from wenet (#427)

sherpa-onnx/csrc/online-ctc-decoder.h

@@ -0,0 +1,42 @@
+// sherpa-onnx/csrc/online-ctc-decoder.h
+//
+// Copyright (c)  2023  Xiaomi Corporation
+
+#ifndef SHERPA_ONNX_CSRC_ONLINE_CTC_DECODER_H_
+#define SHERPA_ONNX_CSRC_ONLINE_CTC_DECODER_H_
+
+#include <vector>
+
+#include "onnxruntime_cxx_api.h"  // NOLINT
+
+namespace sherpa_onnx {
+
+struct OnlineCtcDecoderResult {
+  /// The decoded token IDs
+  std::vector<int64_t> tokens;
+
+  /// timestamps[i] contains the output frame index where tokens[i] is decoded.
+  /// Note: The index is after subsampling
+  std::vector<int32_t> timestamps;
+
+  int32_t num_trailing_blanks = 0;
+};
+
+class OnlineCtcDecoder {
+ public:
+  virtual ~OnlineCtcDecoder() = default;
+
+  /** Run streaming CTC decoding given the output from the encoder model.
+   *
+   * @param log_probs A 3-D tensor of shape (N, T, vocab_size) containing
+   *                  lob_probs.
+   *
+   * @param  results Input & Output parameters..
+   */
+  virtual void Decode(Ort::Value log_probs,
+                      std::vector<OnlineCtcDecoderResult> *results) = 0;
+};
+
+}  // namespace sherpa_onnx
+
+#endif  // SHERPA_ONNX_CSRC_ONLINE_CTC_DECODER_H_